1. Field of the Invention
This invention relates to a thin film magnetic head, and more particularly, to a thin film magnetic head having a pair of magnetic poles formed on a substrate through a magnetic gap layer.
2. Description of the Related Art
A thin film magnetic head comprises a gap portion which is composed of a magnetic pole in the shape of a film formed on a substrate, a magnetic gap layer formed above the magnetic pole, and another magnetic pole in the shape of a film. A thin film magnetic head is formed by covering the gap portion with a protection layer. An end surface of the gap portion in the thin film magnetic head is allowed to face a magnetic medium so as to form a magnetic circuit by one magnetic pole, the magnetic medium and the other magnetic pole, and recording and read back for the magnetic medium are performed by making use of a magnetic variation occurring in the magnetic circuit. Thus, the recording/read back characteristics of the thin film magnetic head are largely dependent on the shape and size of one and the other magnetic poles in the gap portion.
The magnetic poles in the thin film magnetic head have been heretofore formed by various methods including a method of forming one and the other magnetic poles by sputtering using a mask, a method of forming one and the other magnetic poles of a predetermined size by ion milling after deposition, and a method of forming one and the other magnetic poles of a predetermined size by chemical etching after deposition by plating and so on. These conventional methods have problems in respect of working precision, impurity deposition and side etching or the like.
Further, since a track width (corresponding to a width of a magnetic recording line of a magnetic medium) in the gap portion of the thin film magnetic head is in need of being remarkably reduced to, for instance, 2 to 4 .mu.m for higher recording density, it is difficult to manufacture one and the other magnetic poles of uniform width in case of applying deposition to formation of the magnetic poles, and besides, it is difficult to align one and the other magnetic poles, so that it is hard to form the thin film magnetic head having a track width of a predetermined size by forming one and the other magnetic poles of uniform width. Thus, according to the conventional thin film magnetic head, one magnetic pole is formed wider than the other magnetic pole to hold down a variation of the track width caused by positional deviation or the like. However, the thin film magnetic head having both the magnetic poles different in width from each other causes a leakage magnetic field between the opposite edges of both the magnetic poles, resulting in occurrence of side-fringing unfavorable for magnetic recording and read back.
As a configuration to prevent side-fringing from occurring in the thin film magnetic head by making both the magnetic poles of uniform width, there is known a thin film magnetic head, in which impurities are added to one magnetic pole to make both the magnetic poles of substantially uniform width (Japanese Patent Application Laid-open No. 5-189720), or a thin film magnetic head, in which both the magnetic poles in the gap portion are cut in a size of a track width by etching (Japanese Patent Application Laid-open No. 5-303719).
Further, to meet the required precision of both the magnetic poles with demands for smaller size and higher density, there is proposed a thin film magnetic head having a track width regulating member adapted to make both the magnetic poles of uniform width. FIGS. 12 and 13 are schematic views showing conventional thin film recording heads each having a track width regulating member. As a matter of convenience, the description will now be given on the assumption that a reference position is at the substrate side.
In the thin film magnetic head (Japanese Patent Application Laid-open No. 5-342527) shown in FIG. 12, one magnetic pole 102 is formed on a substrate 101, and a non-magnetic film 108 is then formed on the opposite sides of one magnetic pole 102. Subsequently, a magnetic gap layer 103 and the other magnetic pole 105 are formed by sputtering between the non-magnetic films 108 by using the non-magnetic films 108 as a track width regulating member.
Further, in the thin film magnetic head (Japanese Patent Application Laid-Open No. 8-180323) shown in FIG. 13, a pair of track width regulating members 118 are provided at an interval corresponding to a track width (Tw) on one magnetic pole 112 formed on a substrate 111, and one magnetic pole 112a, a magnetic gap layer 113 and the other magnetic pole layer 115 are formed between the track width regulating members 118 to define a gap portion.
In the conventional thin film magnetic heads described above, although the upper and lower magnetic poles of uniform width may be formed by using the track width regulating members, these thin film magnetic heads have problems in respect of precision in film formation and undershoot output. Further, it is difficult to meet a demand for smaller track width.
For instance, in the thin film magnetic head shown in FIG. 12, the track width is determined depending on the width of one initially-formed magnetic pole 102. Further, it is necessary to form a taper portion 104 by machining on each non-magnetic track width regulating film 108 for the purpose of allowing the other magnetic pole 105 to satisfactorily deposit on the non-magnetic track width regulating films 108 by sputtering. Thus, depositing and machining skill of high order is required for forming the non-magnetic track width regulating films 108 with required precision. Further, pole surfaces 105a, 105b of the other magnetic pole in the gap portion are parallel to each other. This parallel portion causes undershoot output.
Further, in the thin film magnetic head shown in FIG. 13, a groove of a track width is formed in the track width regulating member 118 by etching or the like, and the magnetic gap layer 113 and the other magnetic pole 15 are formed in the groove. Since the other magnetic pole 115 is received in the groove of the track width regulating member 118, it is difficult to increase the size of the track width regulating member 118 in a direction of array of the magnetic pole and the magnetic gap layer when a small track width (Tw) is required. That is, the lower limit of the track width is determined depending on the size (H) of the track width regulating member. Thus, it is difficult to form a thin film magnetic head meeting a demand for smaller track width.